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The paper introduces a knowledge-based statistical approach to tolerance allocation, where a systematic analysis for estimating process capability levels at the design stage is used in conjunction with statistical methods for the optimization of tolerances in assembly stacks. The analysis employs detailed knowledge on the tolerance capability of a wide range of manufacturing processes, including the effects of material and design geometry, enabling realistic tolerance distributions to be modeled for key characteristics on designs. The optimization of tolerance stacks is based around achieving the lowest assembly standard deviation for the largest possible and most appropriate component tolerances. The method takes into account failure severity through linkage with Failure Mode & Effects Analysis (FMEA) for the setting of realistic capability targets. The application of the method is fully illustrated using a case study from the automotive industry.

Conformability Analysis is a structured technique which seeks to identify potential problems in the manufacture and assembly of the parts and expresses the outcome as a cost of quality for the design. The analysis provides process capability estimates based on key features of parts. Considerations of the severity of possible failure of each part enables this process risk to be mapped onto a cost model to assess the expected cost of failure. Given the very high proportion of product cost determined very early in a project, and the typically significant quality costs incurred, such an approach to design evaluation is important in the product introduction process. Applications illustrate how the method is used to evaluate, compare or generate designs and show how awareness of process capability is raised in the team and in discussions with suppliers.

This paper points out the importance of advanced design and development techniques in producing vehicles that meet the demand for greater capacity, utility, ease of operation, and operator comfort. The design approach is broken down into four stages and each is discussed with reference to various factors such as materials strength and working stresses. Design evaluation is treated in relation to load and structural strength. These techniques produce an efficient and economical product, and as the authors emphasize, companies that use them have a definite advantage over competitors who still retain the cut and try methods.